I'm having problems getting my mast straight when I follow the directions for pre-bending. The anchor plate and pin (where the left and right diamond wires re-join at the bottom of the mast), immediately after setup in my garage, is centered. When I return to the beach the anchor plate and pin is no longer centered on the mast. This would mean that the top of the mast, about 26 feet away, is falling off to one side, spilling air, right?

I've noticed that in light air that the boat performs better on one tack than the other, when sailed against a boat in close proximity. Thinking through the aerodynamics, the mast appears to be spilling air from the top of the sail on port tack.

Here's my process. I set the the diamond wire adjuster (adjuster on the left diamond wire, as you face the front of the mast) such that the mast ends up straight after I prebend the mast. To sense if the mast is straight I tie a snap line to the bottom of the mast (but not to the top), pull it really tight, and align it with the top of the mast. Then, if the snap line is not centered in the middle of the mast the diamond wire adjuster is ether to tight or too loose. I let out the prebend, re-adjust the diamond wire, and then prebend the mast again until the snap line is centered at the middle. At the conclusion of this the anchor plate and pin is always centered in the middle of the mast.

Great! I put it on the boat and go for a sail, tacking and jibbing several times. On return the anchor plate and pin have moved, consistently to the same side, so far.

This would imply that loading the mast with aerodynamic pressure exposes an unbalanced diamond wire setup or that all rigs have some natural backlash that is difficult to account for in the garage. Loading the mast gives the setup a kick and it shows up. It does not take much offset in the anchor plate to create a significant amount of spillage at the top -- I've played with this.

I'm not doing this right. Is there another way to do the setup? Or, after I get back, what do I need to do to adjust the mast to get it straight?

Thanks Jeremy. These are the in fact the directions I'm following. As well as another set that are little more specific. Both sets do not really address getting the mast straight, unless the wire tension gauge is sensitive enough to pick up an asymmetrical tension in the two diamond wires.

I would suggest an iterative method. Setup as you describe and go sailing. If the mast goes to the left side (seen from the front), release tension on the diamonds, release one turn on the left adjuster and go back to usual diamond tension, Go sailing again, if it still goes to the left, release another turn. If it goes to the right, increase half turn, etc. Continue to the point where your mast stays straight after sailing.

one more thing...the wires have an adjustment turnbuckle on one side...this is to even out both side...this is critical to make sure they are even...that's what makes it bow one way or the other...this process takes some time, and you need to loosed the wires to adjust it and then re-tighten to look if its straight.

J_Eaton: I put the mast on some thin saw horses, facing up. So there is not much in contact with the saw horse and nothing on the ground. And, I use a carpenters square to make sure that the the spreaders are square to the mast, in all directions. I also carefully count the number of turns on the spreader rake to make sure that the spreaders are raked an equal amount. I have never used a Loos gauge, although I own the older type of gauge. I've always looked for straightness using the snap line.

Jacque and Claus: Yes, I adjust turnbuckle on the side diamond wire to make sure that the diamond wires are even. And I know that I have to release the tension on the diamond wire before adjusting and then have to retighten. I do all of that and it does take a great deal of patience and time.

Do you guys eyeball the mast for straightness? Or do you use something like my snap line to measure straightness? Or, is my snap line approach not going to work? Maybe you are using the Loos gauge?

Is it legitimate to judge, after a sail, the straightness of the mast using the diamond wire position relative to the center of the mast? Or, is this flawed?

Otherwise, I may have do what Claus recommends. After a sail loosen the prebend, turn the diamond wire turn buckle to correct evenness, and then retighten the prebend. Hopefully if I resort to this I can leave the mast up?

You're doing the right things by using the Tiger tuning guide. Setting the spreader rake and mast pre-bend does take patience. You will make adjustments several times...tightening or loosening the side diamond wire turnbuckle, then tightening the main diamond wire turnbuckle on the mast to the desired pre-bend tension. With the mast supported by one sawhorse above the main tang and mast track facing up (spreaders horizontal with no biased loads), grab the mast base and eyeball the mast track from base to masthead. If it is not perfectly straight you'll need to repeat the whole process over again until you get it right. Do this with the mast on sawhorses not stepped on the boat. A rigged mast could have a load biased to one side making a fine adjustment very hard. Once you have the diamond wires at equal lengths (this IS key) with the mast track absolutely straight, making pre-bend adjustments with the mast up is OK. Once you've stepped your mast, take a baseline diamond wire tension measurement with a Loos gauge for future reference.

Check your pre-bend by laying the mast on its side (spreaders vertical..using the sawhorses), then really tighten the main halyard hard (be sure there is no interference with the halyard from the mast top to the mast base) and measure the distance between the main halyard and mast track. Gravity may cause the halyard to sag a bit in the middle but it will still be straight in the axis your measuring. Adjust the main diamond wire turnbuckle until you reach your desired measurement.
Good Luck.
John

Yes, I agree -- even diamond wires are key to this problem. I also believe that some twist might occur if the the spreaders are not racked evenly.

In regard to your setup suggestions I believe I'm following them 100%. Strange results I'm getting, however. I in fact do multiple things. I eyeball the mast -- it is straight. I have other people eyeball -- it is straight. Then I added checking it with a snap line to remove any eyeball errors -- it is straight. Under both approaches I have to keep repeating the process to get it straight, with the mast always on the saw horses. When I complete this on the saw horse, I look now at where the diamond wires re-join at the bottom of the mast, and they are centered on the mast.

When I sail the new setup the mast moves as judged by where the diamonds re-join and position relative to the mast.

I getting from this thread that the general thought is that I don't have it straight, and I believe that. And, that people are not doing anything extraordinary to get it straight -- eyeball and repeating tweaks. Maybe I'm missing a very subtle straightness-cue, but I would think that a snap line would be a much more senistive tell tale than eye balling it.

I imagine I will have to follow the iterative approach -- adjust, sail, drop the mast, adjust -- but dropping the mast is very time consuming. I was hoping someone had a really senistive, accurate method or means to measure straightness that would get it right without loading the sail.

Subtle differences in the rake of each of your spreaders can cause one side of the diamond wires to be longer than the other. I think you did the right thing by counting threads...but I counted turns by bottoming out each rake adjuster then backing off an equal number of turns on each side. Any difference between the two can cause the mast to track one direction or the other when tightening the main diamond wire turnbuckle.

I bottomed them out also. Then carefully count up. I'm trying to imagine how that would not work -- possibly unequal bolt length so that the initial starting point is off or maybe threads off slightly. I've imagined building a jig to check this, but I have not come up with anything simple.

I'm faintly aware of the old spreaders, so I believe I have the new ones. Purple housings on a threaded bolt attached fairly close to the mast (boat is at the lake, 2 hrs away so I can't run out and check or take a picture).

Sounds like you have the new style. With everything being square and equal you should be OK. The mast will bend away somewhat if the wind is up or if your flying the spin...especially above the main tang. Remember to use your main as your back stay...otherwise you may experience catastrophic mast failure.

The last check I did was to measure the spreader rake using a straight edge placed across the diamond wires next to the spreaders. Measure the distance from the straight edge to the mast track. Then measure the pre-bend using the process I described earlier with the taunt main halyard. A general rule of thumb (for a medium setting) is for the spreader rake measurement to equal the pre-bend measurement. For me it's about 1 3/8" for both. The diamond wire tension is approximately 800-850 lbs per my Loos gauge. These settings work very well for my crew and I with a combined weight of 345 lbs.

Thought everyone might want to hear the results. I measured the distance from the track to the spreader notch where the diamond wire is positioned -- the spreaders were off by 1/12 of an inch. Apparantly the spreader adjusters have differences after produced. You have to measure. After correcting the spreaders, the diamond wires centered on the mast and stayed there.

I had no need to adjust the turnbuckle on the onside of the diamond wire from the existing setting. I had multiple friends sight down the mast with an unaided eye and then with a snap line. Without a snap line my friends claimed the mast bent off after tightened, but each all saw different directions. With the snap line they all saw the same thing -- "perfectly straight."

I have the mast set at 1.5 inches and I'm reading 48 on my loos gauge, on both sides. This is the first time I've used the Loos gauge.